1. Field of the Invention
The present invention relates to wellbore completion. More particularly, the invention relates to a system of completing a wellbore through the expansion of tubulars. More particularly still, the invention relates to a tubular that can be expanded into another tubular to provide both sealing and mechanical slip means while protecting a polished bore receptacle sealing surface.
2. Description of the Related Art
Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a section of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus known in the art, the casing is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed, or xe2x80x9chungxe2x80x9d off of the existing casing by the use of slips which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever-decreasing diameter.
In one well completion scheme, a well is completed by cementing and then perforating the casing to provide a fluid path for hydrocarbons to enter the wellbore. Hydrocarbons flow from the formation and are urged into a screened portion of production tubing within the casing. Because the annulus between the liner and the production tubing is sealed with packers, the hydrocarbons flow into the production tubing and then to the surface.
In another well completion scheme, the bottom portion of the last string of casing, or liner, is pre-slotted or perforated. In this arrangement, the liner is not cemented into the well, but instead serves as a primary conduit for hydrocarbons to flow back to the surface for collection. In these wells, the upper end of the perforated liner is hung off of an upper string of casing within the wellbore. A string of production tubing is then xe2x80x9cstungxe2x80x9d into the top of the liner to receive and carry hydrocarbons upwards in the wellbore. In this manner, the liner is sealingly xe2x80x9ctied backxe2x80x9d to the surface.
Known methods for tying a string of production tubing into a downhole liner typically involve the use of a tool known as a polished bore receptacle. The polished bore receptacle, or PBR, is a separate tool which is typically connected to the top of the liner by a threaded connection. The PBR has a smoothed cylindrical inner bore designed to receive the lower end of the production string. The production tubing is landed in the PBR in order to form a sealed connection between the production tubing and the liner.
Methods are emerging which involve the expansion of tubulars in situ. In addition to simply enlarging a tubular, the technology permits the physical attachment of a smaller tubular to a larger tubular by increasing the outer diameter of the smaller tubular with radial force from within. The expansion can be effected by a shaped member urged through the tubular to be expanded. More commonly, expansion methods employ rotary expander tools which are run into a wellbore on a working string. Such expander tools include radially expandable members which, through fluid pressure, are urged outward radially from the body of the expander tool and into contact with a tubular therearound. As sufficient pressure is generated on a piston surface behind these expansion members, the tubular being acted upon by the expansion tool is expanded into plastic deformation. The expander tool is then rotated within the expandable tubular. In this manner, the inner and outer diameters of the tubular are increased in the wellbore. By rotating the expander tool in the wellbore and translating the expander tool axially in the wellbore, a tubular can be expanded along a predetermined length.
It is desirable to employ expansion technology in connection with wellbore completions which utilize polished bore receptacles. A known arrangement for a PBR would place the PBR above a section of casing to be expanded. The upper section of the lower string of casing would be expanded into frictional engagement with an upper string of casing. Such an arrangement is shown in FIG. 1.
FIG. 1 illustrates a wellbore 5 completed with casing 15, and also having a lower string of casing, or liner 10, therein. In this Figure, an upper portion of the liner 10 has been expanded in situ into contact with the surrounding casing 15. In this manner, the liner 10 has been frictionally hung in the wellbore 5. The liner 10 includes a polished bore receptacle (PBR) 25 disposed above the expanded section of tubular. The PBR 25 is later used as a sealed coupling to a string of production tubing (not shown).
There are disadvantages to the use of the PBR arrangement shown in FIG. 1. First, it is noted that the PBR is exposed at the uppermost portion of the liner 10. In this position, the polished bore receptacle 25 is susceptible to damage as other downhole tools are run into the wellbore 5. In this respect, downhole tools being run through the PBR 25 most likely would impact the upper surface of the polish bore receptacle 35 on their way downhole, causing burrs or nicks that would hinder the sealing ability of the PBR 25. In much the same way, a slightly misaligned run in string may pass the polish bore receptacle upper surface 35 and damage the interior sealing surface 30. Nicks or burrs on the polish bore receptacle interior sealing surface 30 reduce the effectiveness of later sealing operations.
Downhole tools and run in strings are not the only sources of potential PBR sealing surface 30 damage. Drilling debris, such as residues from cementing the liner 10 into the borehole 5, also have the potential to degrade PBR sealing surfaces 30. Moreover, the position of the PBR 25 in the upper portion 20 of the liner 10 increases the likelihood that the removal of drilling debris and residues will have a deleterious impact on polished bore receptacle seal reliability.
There is a need, therefore, for a method of expanding a tubular such as a string of casing into contact with another string of casing therearound, and which employs a polished bore receptacle without harming the integrity of the PBR. There is a further need for a method and apparatus for providing a polished bore receptacle into a wellbore liner that protects the PBR sealing surfaces, thereby improving seal reliability.
The present invention provides apparatus and methods for providing a polished bore receptacle within an expandable liner for wellbore completion. The invention includes a liner member having an upper expandable section, and then a lower portion which defines a polished bore receptacle. In one aspect, the expandable section includes a sealing member and a slip member around its outer surface. In another aspect, the inner diameter of the liner above the PBR is configured to protect the sealing surfaces of the polished bore receptacle during wellbore completion.